FIG. 7 is a block diagram showing the structure of a processing time measuring device such as the one depicted in Non-Patent Document 1. The processing time measuring device shown in FIG. 7 is structured with a network interface (network I/F) 701, a Ping message transmitting section 702, a Ping message transmitted time recording section 703, a Pong message received time recording section 705, and a processing time computing section 704.
With the processing time measuring device shown in FIG. 7, the Ping message transmitting section 702 transmits a Ping message at an arbitrary time via the network I/F 701. The Ping message transmitted time recording section 703 records the transmitted time at which the Ping message is transmitted by the Ping message transmitting section 702. The Pong message received time recording section 705 records the received time of the Pong message received via the network I/F 701. The processing time computing section 704 compares the transmitted time of the Ping message with the received time of the Pong message, and takes the difference thereof as call processing time of an SIP server or the like that is a measurement target.
Note that a message transmitted from a measurement main body towards the measurement target is called a Ping message. A message returned from the measurement target when the Ping message arrives at the measurement target is called a Pong message. That is, the Ping message is a special message that is to be returned from the measurement target. Typically, the Ping message is structured by including an instruction to return a response for the message explicitly or structured to cause an error so that an error message is returned.
The measurement main body can detect the active/inactive state of the measurement target by receiving the Pong message. Further, the measurement main body judges the measurement time that is a difference between the transmitted time of the Ping message and the received time of the Pong message as the propagation time of the network and the processing time in the measurement target. Assuming that the propagation time of the network is so short that it can be ignored, the measurement time can be considered equal to the processing time in the measurement target. That is, the processing time of the measurement target can be measured by using the Ping message and the Pong message.
As shown in FIG. 8, the Ping message is transmitted to a neighboring node (e.g., a relay server such as an SIP server which communicates with the measurement main body in the network). In a case shown in FIG. 8, node A is the measurement main body, and node B neighboring to the node A is the measurement target. The node B that is the neighboring node performs reception processing of a message. In the reception processing, the node B reads out processing information from a header part of the message, and identifies whether or not to return the message. When judged that it is necessary to return the message, a message is returned as a Pong message. The Ping message can designate a return node. That is, it is also possible to designate the node to which the Pong message is to be transmitted in accordance with the Ping message.
Non-Patent Document 1 shows an example which implements Ping messages with ICMP (Internet Control Message Protocol) and Pong message with ICMP ECHO REPLY. With SIP, (Session Initiation Protocol), it is known to form Ping messages by properly setting transferable-number parameters called “MaxForwards”. When “MaxForwards” reaches “0”, transfer cannot be done any more. As a result, an error message is to be returned. This error message is used as a Pong message.
Non-Patent Document 1: W. Richard Stevens “TCP/IP Illustrated, Volume 1” Addison-Wesley Publishing Company, 1994, pp. 85-96